We previously reported on an issue where error message number 1603 occurs when attempting to restore the iPhone. In these cases, iTunes will deliver the message "The iPhone could not be restored. An unknown error occurred." In our prior coverage, we noted that this can sometimes be resolved by removing the iPhoneâ??s SIM card, then connecting it to your computer.

Apple has now acknowledged this issue in Knowledge Base article #305868 and offered some workarounds including: